Underwater Noise and Endangered Species

Photo Credit: NOAA

by Amy R. Scholik-Schlomer

Humans and other terrestrial animals live in a world of colorful and varying landscapes, appreciated most commonly by the sense of sight. The marine environment is very different in many ways, and hearing has become the predominate means of sensing the underwater world. If one listens carefully, it is possible to grasp the complexity and diversity of the marine "soundscape" and its importance to the species that use sound to sense their environment. It also does not take long to comprehend the power of human-created (anthropogenic) noise to alter these soundscapes.

Since light does not travel far in water and sound does, the ability to accurately assess the underwater environment acoustically is essential to the survival of many marine species. A diverse array of oceanic species, especially marine mammals and fishes, have developed unique ways of relying on sound. Marine mammals in particular use sound in many ways. For example, humpback whales (Megaptera novaeangliae) produce intricate songs to communicate and attract mates, while sperm whales (Physeter macrocephalus) use powerful clicking sounds to locate deep-water prey via echolocation. Simple sounds produced by many fishes and invertebrates, even though they are not as impressive to our human ears, color and shape the marine soundscape, as well. For instance, scientists hypothesize that unique sounds produced from the normal hustle and bustle at coral reefs by its inhabitants help larval fishes find their way home to settle. Furthermore, being able to listen is often as important as producing sound. Many marine mammals and fishes are believed to listen to their surrounding soundscapes in order to perform critical life functions, such as detecting changes in their environment, evading predators, finding prey, and locating others of their species.

The marine underwater soundscape is complex and inherently loud as a result of natural sounds (such as wind, rain, underwater volcanic activity). Anthropogenic sources of sound can also significantly contribute to the soundscape but are often considered noise (unwanted sound). Many human activities produce sound intentionally for a particular purpose, such as to detect objects and aid in navigation (sonar) or find oil and gas deposits (seismic), or unintentionally as a by-product of normal operations (e.g., construction, pile driving, and shipping). These noise sources can be quite diverse in the frequency range (pitch) of sound they produce, their overall sound level (typically measured in decibels), and spatial (e.g., source can be mobile or stationary) and temporal (e.g., noise can be continuous or intermittent) extent. Most of these human activities are essential to our normal way of life in terms of national defense, commerce, transportation, energy, and recreation. As these activities continue to increase, so will noise levels.

Humpback whales.

Photo Credit: Louis Herman/NOAA Sanctuaries Collection

Anthropogenic noise is an ever increasing dominant feature of the marine soundscape. Whether it is a North Atlantic right whale (Eubalaena glacialis) feeding outside Boston, Massachusetts, near one of the busiest shipping lanes in the world or a Chinook salmon (Oncorhynchus tshawytscha) migrating past pile-driving activity that helps to stabilize bridges in the face of earthquakes on the west coast, these already highly vulnerable organisms must adjust and adapt in order to survive. This adaptation can be something as simple as learning to "speak up" when a commercial ship goes by to having to alter migratory patterns to avoid extremely loud areas with the potential to cause hearing impairment. Impacts can range from minor annoyances and increases in stress to major adjustments in their natural patterns. For endangered and threatened species, anthropogenic noise places an additional burden on their already complicated world. The long-term impacts and ultimate fitness consequences of these adjustments are what terrestrial managers and scientists are struggling to better comprehend and appreciate from the point of view of our marine counterparts.

Scientific research on the impacts of noise, as well as the means to mitigate for these impacts, has been growing and becoming more sophisticated. Recent research has included examining the potential of underwater noise to cause physical injury, impact hearing, and elicit behavioral responses in numerous marine protected species, including marine mammals, fishes, and sea turtles. Through these studies, managers are better able to assess impacts, establish safety zones, and prescribe mitigation measures. As science and knowledge on this issue expands and becomes more complex, policy and management of underwater noise will also evolve.

The marine soundscape is colored with a broad range of natural and humanmade sound sources and home to a diverse range of species, many of which are threatened and endangered as the result of other anthropogenic impacts. To understand better how noise affects protected marine species, in the short- and long-term, requires a better understanding of the diverse range of species and how they rely on and use sound, starting from the smallest shortnose sturgeon (Acipenser brevirostrum) fry to the largest blue whale (Balaenoptera musculus). It also calls for an appreciation for the diverse range of sound sources in the marine environment and an awareness of how these components interact to elicit a range of potential impacts. Only with this broad perspective can managers best provide protection for these endangered and threatened marine species.